Methods for flow optimization in the area of three blade rings, of which the first and the third blade ring may be a guide blade ring or a rotating blade ring and the second blade ring may be, on the contrary, a rotating blade ring or a guide blade ring, are known from the related art.
For example, European Patent EP 0 756 667 B1 purports to describe a method according to the definition of the species for flow optimization in which the relative blade profile positioning between the first and the third blade rings is referred to as “clocking.” The preferred application in this case is guide blade clocking, i.e., the first and the third blade ring are guide blade rings, whereas the second blade ring is a rotating blade ring. The principle of the method is that the flow paths of the wakes of the blade profiles of the first blade ring are ascertained up to the entry into the third blade ring and the inlet edges of the blade profiles of the third blade ring are positioned within a predefined tolerance angle range (25% of the blade pitch angle) relative to the inlet positions of the wakes. A direct/centered impact of each wake on the particular inlet edge should be the optimum. Each wake starts as a contiguous turbulent flow from the outlet edge of the blade profile of the first blade ring and is, on its way through the second rotating blade ring, divided into separate portions which move side by side on definite paths. The number of paths corresponds to the perimeter of the flow surface divided by the number of blades of the first blade ring. The moving portions of adjacent wakes of the first blade ring move on these paths in succession. According to the patent, the wake portions are averaged over time so that, mathematically, a contiguous wake is formed again which impacts the third blade ring. A further simplifying assumption of the patented method is that the flow of the wakes through the second blade ring should take place on only one flow surface and it is not taken into account that the wake also has a different configuration radially.
The accuracy and thus the precision of the method suffer from all these simplifying assumptions and approximations.
European Patent EP 1 201 877 B1 also relates to a method according to the definition of the species for flow optimization which is explained using the example of two guide blade rings, which are to be positioned relative to one another, with one rotating blade ring coaxially situated between them. During passage of the wakes of the first blade ring through the moving second blade ring, only the thermodynamic and hydrodynamic conditions on the intake side of the blade profiles of the second blade ring are considered. It is stated that the wake portions passing there interact with the blade boundary layer on the intake side and change in such a way that at least two zones, spaced from one another, are identifiable, these zones differing in at least one thermodynamic or hydrodynamic characteristic. The magnitude of the entropy is mentioned as a preferred discrimination criterion. However, it is also stated that there may be additional parameters, which differ in their magnitude, without specifying them in detail. In any event, one of the identified zones is to be selected and guided onto the intake edges of the blade profiles of the third blade ring. The at least one non-selected zone may fit in the blade profile space. Admittedly it may be necessary to analyze different parameters. It may also be necessary, for example, to guide first the zone of greater entropy and then the zone of smaller entropy onto the intake edges and to ascertain mathematically/experimentally which measure results in an increase in efficiency. This patent basically teaches a trial and error principle which compels those skilled in the art to adopt multiple different measures.